DESCRIPTION: The acquisition of a mature "theory of mind" is a major achievement of the preschool years. The changes that occur at around age four years are profoundly important in three separate domains: cognition, social understanding, and language. The understanding that other persons have knowledge and beliefs different one's own and that those beliefs can be true or false is a major breakthrough in conceptual understanding and representational ability. Existing research fails to determine whether language plays a critical causal role in the ontogenesis of this theory of mind, since no population has been tested that lacks language during the critical years. In addition, the tasks used almost all require language for understanding the stories. The investigators propose to use a variety of verbal and nonverbal tasks to test the development of false belief understanding in oral profoundly deaf children, whose language development is significantly delayed. In contrast, deaf children learning American Sign Language (ASL) as a first language should pass ToM tasks on a normal timetable. We will explore the prerequisites for developing a ToM in deaf children raised in different social and linguistic circumstances, aged between 3 and 7 years, compared to hearing controls. The research proposed here has both theoretical and educational significance. Theoretically, the project will test three different hypotheses concerning the relationship of language and ToM development. Educationally, it is of central importance to understand the experiences necessary for a ToM, since different consequences follow for early deaf education if a mature theory of mind depends on mastery of a full language than if it is a function of cognitive or social maturity alone.